1. Field of the Invention
This invention relates to a novel aromatic polyamide resin having pendant silyl groups the said aromatic polyamide resin has excellent heat-resistance, mechanical strength, electric conductivity and other physical properties as well as excellent solubility in common organic solvents and improved molten processing property.
2. Description of the Related Art
Aromatic polyamide resins are generally referred to as wholly aromatic polyamides prepared from the polymerization of aromatic diamines and aromatic dicarbonyl chlorides.
Especially, they are a sort of special engineering plastic having excellent physical properties, and can be widely used in making belts such as V-belt and conveyer belt, special clothing for fire-proof, various structural materials for electric and electronic products, sports equipments, and packing materials.
They have excellent physical properties such as heat-resistance, hardness of combustibility, resistance to chemicals, and mechanical strength, but there are some problems in plastic processing because more than 400.degree. C. of plastic processing temperature is needed, and melting and decomposition are simultaneously occurred.
Some techniques are reported to overcome the problems of polyamide resins. For example, diamine, which has some flexible structure such as --O--, --SO.sub.2 --, --CH.sub.2 -- between two benzene rings, is used (U.S. Pat. No. 3,767,756), and halogen atom as side chain substituted diamine is also used (U.S. Pat No. 3,671,542).
In addition, it is also reported that heterocyclic structures are introduced in the polymer chain [J. Poly. Sci. Part B4,267(1966)].
But, in the case of the polyamide resin prepared according to the methods hereinbefore, the molten processing property is somewhat enhanced, but heat-resistance and mechanical strength are remarkably reduced.
General methods for preparing polyamide resin include solution polymerization, interfacial polymeriaztion, and direct polymerization. In the method of solution polymerization, dicarboxylic acid is converted to acid chloride and then the said acid chloride is reacted with diamine in solution in the presence of catalyst selected from pyridine, triethylamine, calcium chloride or calcium hydroxide.
The reaction solvent in this case includes amides such as dimethylacetamide (hereinafter denoted as "DMAc"), N-methylpyrrolidinone (hereinafter denoted as "NMP"), hexamethylphosphoric triamide (hereinafter denoted as "HMPA"), and tetramethylurea (hereinafter denoted as "TMU"), but dimethylformamide(DMF) and dimethylsulfoxide can not be used because they react with acyl chloride (U.S. Pat. Nos. 3,287,324, 3,094,511, and 3,354,123).
In the method of interfacial polymerization, acid chloride is dissolved in a solvent such as dichloromethane which is not miscible with water, and polymerized by adding the above acid chloride solution to the aqueous aromatic diamine solution.
In this case, phase transfer catalyst such as trimethylbenzylammononium chloride or base catalyst such as pyridine can be used, if desired.
The aromatic polyamide prepared by interfacial polymerization can be obtained as high molecular weight, but it is not appropriate in preparing fiber or films because of rather higher distribution of molecular weight than in the case of solution polymerization, and moreover reproducibility in experimental results is not sufficient.
Recently, a technique called yamazaki polyphosphorylation is reported for preparing aromatic polyamide easily in the laboratory by direct polymerization.
In the method of said yamazaki polyphosphorylation, aromatic dicarboxylic acid and diamine are directly polymerized using triphenylphosphite and pyridine as condensation catalysts, in NMP, the same solvent as in the case of solution polymerization, and this method is estimated as a considerably improved one compared with the previously developed ones.
In recent times, researches are actively progressed to improve the processing property of aromatic polyamide, for example, polymer having functional group such as carboxyl group, which is similar to ionic polymer(ionomer), is polymerzed using metal ion, and representative example of it is "surlyn" developed by DuPont, U.S.A. Both this method of polymerization is restricted mainly to the method of improving adhesive property of polyolefinic resins.
N. D. Ghatage et al. describe a method to maintain the thermal stability and increase the solubility of polymer by introducing aromatic silane moiety inside the aramid. But, most of the polyamide prepared like this exhibited poor result in solubility.
In another research field, aramid is prepared by connecting pendant group such as phenyl, phenoxy, phenylthio, or phenylcarbamoly group to the silylated polyamide backbone, and in this case the said aramid is known to have more than 200.degree. C. of high glass transition temperature(Tg) and excellent solubility.
We inventors designed to exploit the above mentioned direct polymerization in preparing novel aromatic polyamides, and completed this invention by introducing pendant silyl group to the molecular chain of known aromatic polyamides in order for the polymers to have excellent thermal and mechanical property as well as excellent molten processing property and solubility in solvents.